Electron Spin Resonance and Luminescence Spectroscopic Observation and Kinetic Study of Chemical and Physical Singlet Oxygen Quenching by Resveratrol in Methanol

Electron spin resonance (ESA) spectroscopy and near-infrared (NIR) fluorescence spectroscopy were performed to observe singlet oxygen quenching by resveratrol. Resveratrol greatly decreased the 2,2,6,6-Tetramethyl-4-piperidone-N-oxyl radical signal as determined by ESR spectroscopy. Resveratrol also efficiently decreased luminescence emission at 1268 nm as studied with a NIR spectrofluorometer, showing positive evidence of singlet oxygen quenching by resveratrol. The total singlet oxygen quenching rate constant (k(r) + k(q)) of resveratrol in methanol was determined to be 2.55 x 10(7) M-1 s(-1). The singlet oxygen chemical quenching rate constant (k(r)) of resveratrol was calculated by measuring its reaction rate with singlet oxygen relative to that of alpha-terpinene in the same solution under light illumination. The k(r) value of resveratrol was 1.15 x 10(6) M-1 s(-1). The percent partition of chemical quenching over total singlet oxygen quenching (k(r) x 100)/(k(r) + k(q)) for resveratrol was 5.11%. The results showed that resveratrol quenches singlet oxygen almost exclusively through the mechanism of physical quenching. Resveratrol showed a protective activity similar to that of BHA on the methylene blue sensitized photooxidation of alpha-terpinene. This unambiguously explains the mechanism of how resveratrol protects tissues and cells in biological systems or important nutrients in food systems against their photosensitized oxidations.